Intramolecular particle exchange in the fragmentation of methanol upon valence photo double ionization*

We investigated the valence photo double ionization (54eV) of isolated methanol molecules (CH₃OD and CD₃OH), by measuring the momenta of 2 electrons and 2 cation fragments in coincidence, using the COLTRIMS (COLd Target Recoil Ion Momentum Spectroscopy) technique. In this approach, the momentum of a single neutral fragment is also determined by coincidence ion momentum imaging and momentum conservation. Here we report on the comparison of specific 3-body fragmentation channels in which the reactions show a clear signature of intramolecular particle exchange, which we trace via deuterium scrambling:

(a) CH₃OD+ hv  -> (CH₃OD)*²⁺ + 2e^- -> CHD⁺ + OH⁺ + H + 2e^-

(b) CD₃OH+ hv  -> (CD₃OH)*²⁺ + 2e^- -> CHD⁺ + OD⁺ + D + 2e^-

 

The electronic and nuclear dynamics of dissociative photo double ionization reactions are investigated for the two different isotopologues of methanol. This is achieved through the analysis of the relative branching ratios with respect to the most intense 2-body breakup channel, CH₃⁺ + OD⁺ or CD₃⁺ + OH⁺. Electron-ion energy correlation maps are used to identify and isolate the participating electronic states along the C-O internuclear distance of dication potential energy surfaces, which are calculated using the Multi-Reference Configuration Interaction (MRCI) method. Exploiting the measured electron energy sharing and the electron angular distributions we distinguish between autoionization and direct double ionization. We apply pairwise ionic and neutral fragment momentum sharing, Newton plots, and the native frames analysis to retrace the fragmentation processes and identify intermediates.